From owner-freebsd-acpi@FreeBSD.ORG  Thu May  6 10:47:28 2004
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Date: Thu, 6 May 2004 10:47:28 -0700 (PDT)
From: Nate Lawson <nate@root.org>
To: Mike Silbersack <silby@silby.com>
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cc: acpi@freebsd.org
Subject: Re: power savings and usb
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On Thu, 6 May 2004, Mike Silbersack wrote:
> On Thu, 6 May 2004, Nate Lawson wrote:
>
> > > Gah, except that my experiment in clockswitching made the usb stack mad,
> > > so it's constantly priniting "usb0: X scheduling overruns", where X
> > > appears to be a number containing one or two bits of entropy per second.
> > > I will have to go visit ohci.c with a cluebat when I get a chance.
> > >
> > > Er, it stopped when I plugged in the power cord, and starts again when I
> > > unplugged it.  Is it possible that ohci.c is reading some USB voltage
> > > value instead of the overrun bit that it thinks it is reading?
> >
> > hw.acpi.cpu.cx_supported: C1/0 C2/84 C3/120
> > hw.acpi.cpu.cx_lowest: 1
> > hw.acpi.cpu.cx_history: 9175/0 173443/9175 0/0
> >
> > This means I am requesting a lowest sleep of C2 (idx 1 of the options
> > supported).  The history values show that I haven't used C3 at all and am
> > using C2 at a rate of about 95%.
> >
> > ohci may have problems with C3.  On my uhci, it demotes to C2 without
> > causing problems.  You can override this by setting in /etc/rc.conf:
> >
> > economy_cx_lowest="1"
> >
> > -Nate
>
> Something else must be happening, because:
>
> hw.acpi.cpu.cx_supported: C1/1 C2/99 C3/288
> hw.acpi.cpu.cx_lowest: 0
> hw.acpi.cpu.cx_history: 5558639/0 0/0 0/0
>
> But, since I went and killed the scheduling overrun interrupts at the
> source, we don't need to worry anymore. :)

Interesting.  I'm not sure how the AC transition affected your USB then.

-Nate